The present invention relates to a semiconductor device in which a semiconductor component is mounted on a substrate and to a method of manufacturing the same. More particularly, the present invention relates to a semiconductor device in which a semiconductor component such as, for example, an optical semiconductor component is mounted, which has a surface processed to form a mesa portion with an active region of a semiconductor therein and an electrode on the top of the mesa portion.
With developments in optical communication, there have been demands for inexpensive high-performance modules for optical communication. Particularly, when transmitting image information, a photo-detecting module with high sensitivity over a wide band is required. For obtaining such a module, a pin junction diode (a positive-intrinsic-negative photodiode) or an avalanche phenomenon photodiode (an avalanche photodiode) has been used. Examples of such components have been disclosed in JP 9-213988 A, xe2x80x9cIEEE Photonics Technology Letters vol.2 no.7 pp. 505-506, 1990xe2x80x9d, and xe2x80x9cElectronics Letters, vol.26, no.5, pp. 305-307, 1990xe2x80x9d.
Generally, those components have a so-called mesa portion obtained by allowing an active layer to grow on a semiconductor substrate and removing portions other than necessary portions by etching. In such a structure with a mesa portion, electrodes are provided on the substrate and the top of the mesa portion. However, the active layer is provided directly under the top of the mesa portion and therefore such a component is quite vulnerable to an impact. Therefore, it is difficult to connect the electrode on the top of the mesa portion formed by evaporation or the like to an external electrode with a wire (wire bonding). A semiconductor substrate (a semiconductor component) having an active surface processed to form a mesa portion is mounted on a substrate with a xe2x80x9cface downxe2x80x9d method using solder or the like in many cases.
Conventionally, in order to maintain reliability, generally an optical communication device has been sealed hermetically into a package. This package secures heat-cycle resistance, moisture resistance, or the like. However, as the optical communication comes into common use and comes to be introduced into domestic use, which previously has been limited to commercial use, much significance has come to be given to cost reduction in optical communication devices as in usual household electric appliances. Therefore, it has been required to secure the reliability without using a sealing package hindering the cost reduction.
With respect to the reliability, the greatest consideration must be given to deterioration caused by the heat cycle. Particularly, domestic equipment is switched on only when required, which is different from commercial equipment that is substantially in a working condition constantly. Therefore, the stress caused by the difference in thermal expansion between a semiconductor component and a substrate tends to deteriorate a semiconductor component. Especially, in a photodiode having a mesa portion provided with an electrode in its top portion, the deterioration tends to be remarkable.
Particularly, in the case of using a photodiode, the photodiode has a further smaller number of terminals compared to that in a general LSI, resulting in a heavy load per terminal when mounted. Therefore, the photodiode also tends to be affected by the stress when mounted. However, when the load merely is lightened, a sufficient electrical connection cannot be obtained, thus decreasing production yield.
In view of the above-mentioned circumstances, the present invention is intended to provide a highly reliable semiconductor device. Further, the present invention is intended to provide a method of manufacturing the semiconductor device, particularly a method enabling the deterioration of an element to be suppressed.
In order to achieve the above-mentioned object, a semiconductor device of the present invention includes: a semiconductor component having an active surface processed to form a mesa portion and an electrode formed on a top of the mesa portion; and a substrate on which the semiconductor component is to be mounted. The semiconductor component is mounted on the substrate so that the active surface is positioned on a side of the substrate. On the surface of the substrate, a first bump and a second bump are formed. The second bump is allowed to be higher than the first bump. Thus, the semiconductor component is mounted on the substrate with the first bump being electrically connected to the electrode via a conductive adhesive member without coming into contact with the electrode.
In the semiconductor device, it is preferable that the electrode formed on the top of the mesa portion is taken as a first electrode and a second electrode is formed on the semiconductor component, and the second bump is in contact with the second electrode. According to this preferable embodiment, together with the first bump, the second bump electrically connects the substrate and the semiconductor component while maintaining the space between the substrate and the semiconductor component.
It is preferable that a conductive adhesive member is positioned so as to contact with the second bump and the second electrode, since the reliability of the electrical connection in that location is increased.
In the semiconductor device, it is preferable that a plurality of second bumps are formed and have substantially the same height. The variation in height of the plurality of second bumps is not particularly limited, but suitably is 3 xcexcm or less.
In the semiconductor device, a suitable space between the top of the first bump and the electrode formed on the top of the mesa portion is in a range between 1 xcexcm and 10 xcexcm, particularly between about 3 xcexcm and 5 xcexcm.
In the semiconductor device, at least one selected from, for example, solder and a conductive adhesive can be used as the conductive adhesive member.
In order to achieve the above-mentioned object, a method of manufacturing a semiconductor device of the present invention is a method of manufacturing a semiconductor device including: a semiconductor component having an active surface processed to form a mesa portion and an electrode formed on a top of the mesa portion; and a substrate on which the semiconductor component is to be mounted, with the semiconductor component being mounted on the substrate so that the active surface is positioned on a side of the substrate. The method includes: forming a first bump and a second bump on a surface of the substrate so that the second bump is allowed to be higher than the first bump; transferring a conductive adhesive member at least onto the first bump; mounting the semiconductor component on the substrate so that the first bump does not come into contact with the electrode while electrically connected to the electrode via the conductive adhesive member.
According to the method of manufacturing a semiconductor device of the present invention, it is preferred to form the first bump and the second bump so that the difference in height between the first bump and the second bump is allowed to be greater than the height of the mesa portion.